1. Field of the Invention
This invention relates to a method of aligning a mask and a wafer used for the manufacture of semiconductor circuit elements such as IC, LSI or the like.
2. Description of the Prior Art
Usually, alignment between a mask and a wafer is effected by bringing the alignment marks provided on the mask and the alignment marks provided on the wafer into a predetermined positional relationship to thereby accomplish the alignment between the actual element (circuit) patterns of the mask and the actual element patterns of the wafer. The actual element patterns and the alignment marks of the mask are formed by the use of a photorepeater. That is, the actual element patterns 2 of the mask 1 shown in FIG. 1 of the accompanying drawings are formed by recording a reticle 4 for actual element pattern shown in FIG. 2 by the use of the step and repeat method, and alignment marks 3 are recorded by interchanging the reticle 4 with a reticle 5 for alignment mark shown in FIG. 3. In this case, since the reticle 4 for actual element pattern is interchanged with the reticle 5 for alignment mark, there may be created a positional error of the order of 1 to 3 .mu.m between the actual element patterns 2 and the alignment marks 3. Therefore, when there is a positional error between the actual element patterns 2 and the alignment marks 3, there would be created an alignment error between the actual element patterns of the mask and the actual element patterns of the wafer even if the alignment between the mask and the wafer was effected accurately by the use of the alignment marks of the mask and the alignment marks of the wafer.
For this reason, heretofore, the actual element patterns of the mask and the actual element patterns of the wafer have been adjusted to each other by comparing the actual element patterns of the mask and the actual element patterns of the wafer to detect an amount of deviation between the actual element patterns and the alignment marks after the alignment marks of the mask and wafer have been adjusted to each other, and by moving at least one of the mask and wafer parallel to the other on the basis of the amount of deviation. After the mask pattern has been printed on the wafer, the thus printed wafer is retracted from the mask position and a new wafer, which is the same as the previous wafer with respect to the positional relationship between the actual element patterns and the alignment marks, is supplied to the mask position and in this case, the amount of deviation between the adjustment of the previous alignment marks and the adjustment of the actual element patterns is memorized; the adjustment between the alignment marks of this new wafer and the alignment marks of the mask is effected, whereafter at least one of the mask and the wafer is further moved parallel to the other on the basis of the memorized amount of deviation, whereby the actual element patterns of the mask and the actual element patterns of the wafer are adjusted into a predetermined positional relationship.
Thus, the alignment method of the prior art which involves the adjustment between the actual element patterns of the mask and wafer which are difficult to adjust suffers from a disadvantage that the alignment work is very difficult to do.